A ChamferCut milling cutter (alternatively referred to herein as a ChamferCut tool, milling tool, or milling cutter) is a forming cutter which has a strongly asymmetric profile and which in a continuous form milling process produces chamfers at the tooth edges of a toothed workpiece. The milling cutter furthermore is characterized by a high number of starts. In contrast to a hobbing cutter, a ChamferCut milling cutter operates continuously, but not rollingly.
This means that each tooth of a ChamferCut milling cutter, which gets into a new gap, produces the chamfer along the end face of the toothing. However, this is not effected in several profiling cuts, as in gear hobbing, but by a special profile of this tool which produces the entire contour of the chamfer (both flanks and the tooth base) in one cut.
The ChamferCut milling cutters hence are strongly workpiece-bound. Toothings which are fabricated with the same hobbing cutter (or the same reference profile) also require a separate ChamferCut milling cutter, when the same differ e.g. in terms of helix angle, profile shift or number of teeth.
A tool set for chamfering cylindrical spur gears typically includes two identical ChamferCut tools, one each for the upper and the lower surface of the toothing. It would also be possible, however, to use only one ChamferCut milling cutter when the toothing is to be deburred on one side only or when it is possible to swivel the ChamferCut milling cutter by 180°. For conical toothings, which are to be chamfered on the upper and lower surface, two different ChamferCut tools are necessary.
The two ChamferCut milling cutters are clamped onto the tool arbor with opposite orientations, so that the upper and lower end faces of the toothing are chamfered with opposite directions of rotation of the tool spindle. Hence, a change in the direction of rotation of the tool spindle is required between the two machining steps.
The general method for chamfering a gearwheel with a ChamferCut milling cutter is described in EP 1 495 824 A1. There is described a method for manufacturing a gearwheel from a gear blank, in which the rotatingly driven gear blank clamped in a machine tool is machined with a hobbing cutter arranged on a rotatingly driven tool arbor and the raw gearwheel produced subsequently is deburred by means of a rotatingly driven deburring tool in that the front edges of the tooth grooves are chamfered. The rotational speeds of the deburring tool and raw gearwheel have a constant ratio, wherein the deburring of the raw gearwheel, invariably clamped in the machine tool is effected in a continuous pass by means of a deburring tool similar to a side ChamferCut milling cutter with cutting teeth, which is non-rotatably arranged on the tool arbor of the hobbing cutter, wherein the front edges of the tooth grooves are machined one after the other in the manner of the gear hobbing method, and wherein the tool arbor is moved from the gear hobbing position into a deburring position. Here, however, only the method for producing the chamfers by means of the special ChamferCut tool is described in general.
Since the ChamferCut milling cutter is a setting tool, a positional orientation between the workpiece and the ChamferCut milling cutter must be employed. The tool must be exactly centered onto a gap of the gearwheel by means of a particular reference tooth. This reference tooth must be positioned at an exact distance from the main bearing of the machining head, and at a particular rotary position, so as to meet with one of the end faces of the toothing.
This particularity in the setting of the tool and in the chamfer production of a ChamferCut milling cutter leads to the fact that most of the parameters for the description of the ChamferCut milling cutter are only calculated mathematically, and cannot be measured at the milling cutter. The exact setting data (alternatively referred to herein as “milling cutter data” or “setpoint values”) therefore are provided by the tool manufacturer in special setting data sheets or provided online via a special data exchange interface. In the case of this tool, the theoretically correct setting data can be entered into the machine controller to produce a design-compliant tooth chamfer. The data may be entered into the controller in an electronic data format such as XML. However, when the chamfer now does not correspond to the requested values, the setting values from the data sheet must be modified with reference to measurement values of the chamfer produced.
Since the tool is a forming cutter with a strongly asymmetric profile, it so far has been determined in practice with reference to several experiments with which changed setting data a correct tooth chamfer can be produced. Since a plurality of axes is involved in the chamfer production, the correct setting sometimes turns out to be very difficult.
When chamfering and deburring helical toothings, it is particularly difficult that corrections of the setting data have different effects between the sharp and the obtuse tooth edge.
It now is the object underlying the present disclosure to provide a method with which the correction values for influencing the chamfer size, chamfer shape and chamfer symmetry can be determined with reference to measured or entered data and thereafter the setting data of the gear cutting machine can be corrected correspondingly. With these changed setting data a correct chamfer shape and an appropriate chamfer size and chamfer symmetry will then be produced during the subsequent chamfering and deburring operation.
In a first aspect of the present disclosure, a semi-automatic correction of the chamfer geometry is provided. When the chamfer width is to be changed, the current position of the tool in the vertical direction (Z1-direction) is corrected by the machine operator with a correction amount (see FIG. 4A). In helical toothings, however, this purely vertical Z1-correction has a non-uniform effect between the left and right tooth edges. Therefore, a correction of the rotary position of the workpiece (C1-direction) must be made in addition, whose magnitude and direction depends on the helix angle and the tooth direction of the toothing and furthermore on whether the chamfer is to be produced at the top or at the bottom of the toothing.
According to a first solution of the present disclosure, the machine operator specifies the correction in the Z1-direction (e.g., via input to a user interface), and the NC controller of the machine calculates the necessary additional correction in C1-direction by means of (e.g., as a function of) the tool and toothing data. The machine controller therefore converts the results of the trigonometric functions with which the effect on the chamfer geometry is described into the required movements of different machine axes (linear and rotational) to achieve the necessary correction on the workpiece.
When the chamfer size is to be changed between the left tooth edge and the right tooth edge, a tangential correction of the position of the tool edge with respect to the tooth gap must be effected. There are two possibilities depending on the configuration of the unit.
When the unit has a V1-axis (which is coaxial with the B1-axis), the ChamferCut tool is shifted along its middle axis. The controller then must make additional corrections of the Z1- and C1-axes. The corrections in direction of the Z1-axis are influenced by the swivel angle of the tool, whereas the corrections in direction of the C1-axis are influenced by the transverse pressure angle of the gear.
When the unit on the other hand has a Y1-axis, the entire unit in this case is shifted tangentially to the workpiece. The additional correction then must only be made via the C1-axis, whose size in turn is determined by the transverse pressure angle of the gear. For this purpose, the calculation is effected via trigonometric functions which are obtained from the toothing data and from the dimensions of the required chamfer. For example, the controller may determine a size of an additional correction to be made via the C1-axis as an output of a trigonometric function of the toothing data, the required chamfer dimensions, and the corrections made in the Y1 direction.
A further aspect of the present disclosure is a fully automatic correction of the chamfer geometry according to the result of an externally measured chamfer or according to the value of a chamfer measurement carried out within the machine (e.g., carried out by the a machine internal measurement system and calculated by the controller). The correction mechanisms are identical to the corrections indicated above, except for the fact that in this case the controller additionally must decide with what axis movements the chamfer can be corrected best. The chamfer width here is optionally entered (e.g., entered by the operator via a user interface) or measured (e.g., via a sensor of the measurement system) and the correction is made proceeding from this measurement result (e.g., the controller determines axis movements which will provide the desired correction of the chamfer geometry as a function of measured parameters of the chamfer). The controller of course also offers the possibility to enter (e.g., via a user interface) or measure (e.g., via a sensor) the chamfer depth and/or the chamfer angle and to therefrom determine the correction factors for the axis movements.
With the trigonometric functions utilized above, the controller offers an assistant function to calculate or convert the chamfer depth and/or the chamfer angle to the chamfer width or vice versa. This opens up the possibility for the machine operator to obtain values resulting from easily measurable values (chamfer width) via the machine controller, which then can be compared with values for the chamfer size shown in the corresponding workpiece drawing (alternatively referred to herein as drawing values) and which then in turn can be used for specifying the correction for the chamfers. For example, when only the chamfer depth is specified in the drawing, the chamfer width to be measured can easily be determined therefrom and be output as control value.
In an extension, this output function offers an assistant function to determine the chamfer size for the soft machining of a toothing. The chamfers usually are produced already during soft machining, but must be present in a certain size after hard finishing. According to the prior art, the indications as to the chamfer size usually are provided on the finished part drawing and hence are not available for soft machining. The machine operator now faces the task of determining the correct chamfer size at the workpiece with a known flank overmeasure and of checking the compliance therewith.
Further features, details and advantages of the present disclosure can be taken from the attached representation of a preferred embodiment.